Hot solids gasifier with CO2 removal and hydrogen production

ABSTRACT

A gasifier  10  includes a first chemical process loop  12  having an exothermic oxidizer reactor  14  and an endothermic reducer reactor  16 . CaS is oxidized in air in the oxidizer reactor  14  to form hot CaSO 4  which is discharged to the reducer reactor  16 . Hot CaSO 4  and carbonaceous fuel received in the reducer reactor  16  undergo an endothermic reaction utilizing the heat content of the CaSO 4 , the carbonaceous fuel stripping the oxygen from the CaSO 4  to form CaS and a CO rich syngas. The CaS is discharged to the oxidizer reactor  14  and the syngas is discharged to a second chemical process loop  52 . The second chemical process loop  52  has a water-gas shift reactor  54  and a calciner  42 . The CO of the syngas reacts with gaseous H 2 O in the shift reactor  54  to produce H 2  and CO 2 . The CO 2  is captured by CaO to form hot CaCO 3  in an exothermic reaction. The hot CaCO 3  is discharged to the calciner  42 , the heat content of the CaCO 3  being used to strip the CO 2  from the CaO in an endothermic reaction in the calciner, with the CaO being discharged from the calciner  42  to the shift reactor  54.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. patent application Ser. No.12/239,232, filed Sep. 26, 2008, which is a Continuation of U.S. patentapplication Ser. No. 11/422,703, filed Jun. 7, 2006, now U.S. Pat. No.7,445,649, which is a Continuation of U.S. patent application Ser. No.10/449,137, filed May 29, 2003 now U.S. Pat. No. 7,083,658, which areincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION

This invention relates generally to a method for producing hydrogen.More particularly, the present invention relates to a method utilizingfossil fuels, biomass, petroleum coke, or any other carbon bearing fuelto produce hydrogen for power generation which minimizes or eliminatesthe release of carbon dioxide (CO₂).

Fossil fuel power stations conventionally use steam turbines to convertheat into electricity. Conversion efficiencies of new steam powerstations can exceed 40% on a lower heating value basis (LHV). Newsupercritical steam boiler designs, relying on new materials, allowhigher steam temperatures and pressures, providing efficiencies of closeto 50% LHV and further improvements might be expected. Significantadvancements have also been made in combined cycle gas turbines (CCFTs).A gas turbine can withstand much higher inlet temperatures than a steamturbine. This factor produces considerable increases in overallefficiency. The latest designs currently under construction can achieveefficiencies of over 60% LHV. All of these improvements in efficiencytranslate into a reduction of the specific emissions on a per megawattbasis.

Although substantial reductions in emissions of CO₂ could be achieved byincrease in efficiency of energy conversion and utilization, suchreductions may not be sufficient to achieve atmospheric CO₂stabilization. Therefore, efforts have also been directed towards thecapture and sequestration of the CO₂ emitted by fossil fuel-fired powerplants. Sequestration of CO₂ entails the storage or utilization of CO₂in such a way that it is kept out of the atmosphere. Capture of the CO₂may be performed prior to or after combustion of the fuel. Production ofCO₂ may be minimized during combustion of the fuel.

The fuel may be de-carbonized prior to combustion by extracting H₂ fromthe hydrocarbon fuel, the CO₂ being captured and the H₂ beingsubsequently combusted. Steam reforming, gasification and partialoxidation are examples of such processes. The most promisingde-carbonization approach is via Integrated Gasification Combined Cycle(IGCC). With IGCC, coal is gasified to produce a synthesis gas, which isthen catalytically water gas shifted in order to increase the CO₂concentration. This shifted synthesis gas is quenched, and CO₂ isremoved with a solvent, such as selexol, in a process analogous to theamine flue gas scrubbing. Separated CO₂, is dried and compressed tosupercritical conditions for pipeline transport. The cleaned synthesisgas, now rich in H₂, is fired in a combustion turbine and waste heatfrom the gasification quench and from the GT fuel gas is recovered toraise steam and feed a steam turbine. Because the CO₂ is removed fromthe concentrated and pressurized synthesis gas stream, the incrementalcapital cost and energy penalty is lower than for the capture of CO₂from flue gas. A study by Parsons Energy and Chemical Group, Inc. hasshown an incremental energy penalty of about 14% and the cost of CO₂mitigation of about $18/tonne (Owens, et al., 2000).

Combustion of the fossil fuel in O₂/recycled flue gas eliminates theneed for capture of CO₂ by using pure or enriched oxygen instead of airfor combustion. A substantial energy penalty is incurred using thisprocess due to the large power requirements of producing pure oxygen.

Alternatively, separation of CO₂ after combustion with air can beaccomplished by a variety of techniques. The most well establishedmethod today is removal from the flue gas stream by amine solventscrubbing in an absorption-stripping process. Such processes are alreadyapplied commercially to coal-fired boilers for the purpose of producingCO₂ for industrial or food industry use. Unfortunately, substantialcapital equipment is required. The efficiency of the power plant issignificantly reduced by the energy required to regenerate the solvent.Studies of amine scrubbing technology applied to a U.S. utility boilercase indicate that capital investment is on the order of the originalpower plant and energy efficiency is reduced by 41%.

SUMMARY OF THE INVENTION

Briefly stated, the invention in a preferred form is a method forproducing a gas product from a carbonaceous fuel which comprises a firstchemical process loop including an exothermic oxidizer reactor and anendothermic reducer reactor. The oxidizer reactor has a CaS inlet, a hotair inlet and a CaSO₄/waste gas outlet. The reducer reactor has a CaSO₄inlet in fluid communication with the oxidizer reactor CaSO₄/waste gasoutlet, a CaS/gas product outlet in fluid communication with theoxidizer reactor CaS inlet, and a materials inlet for receiving thecarbonaceous fuel. CaS is oxidized in air in the oxidizer reactor toform hot CaSO₄ which is discharged to the reducer reactor. Hot CaSO₄ andcarbonaceous fuel received in the reducer reactor undergo an endothermicreaction utilizing the heat content of the CaSO₄, the carbonaceous fuelstripping the oxygen from the CaSO₄ to form CaS and the gas product. TheCaS is discharged to the oxidizer reactor, and the gas product beingdischarged from the first chemical process loop.

When the gas product is a CO rich syngas, the method further comprises asecond chemical process loop including a water-gas shift reactor havinga syngas inlet in fluid communication with the reducer reactor CaS/gasproduct outlet. The shift reactor also has a CaO inlet, a steam inletfor receiving gaseous H₂O, and a particulate outlet. A calciner has aCaCO₃ inlet in fluid communication with the shift reactor particulateoutlet and a CaO outlet in fluid communication with the shift reactorCaO inlet. The CO of the syngas reacts with the gaseous H₂O to produceH₂ and CO₂, the CO₂ being captured by the CaO to form hot CaCO₃ in anexothermic reaction, the hot CaCO₃ being discharged to the calciner, theheat content of the CaCO₃ being used to strip the CO₂ from the CaO in anendothermic reaction in the calciner, and the CaO being discharged fromthe calciner to the shift reactor.

The shift reactor may also have a fuel inlet for receiving thecarbonaceous fuel. In this case, the CO of the syngas and thecarbonaceous fuel reacts with the gaseous H₂O to produce H₂, CO₂, andpartially decarbonated, hot carbonaceous particulates, with the hotcarbonaceous particulates being discharged to the reducer reactor.

The oxidizer reactor may also have a particulate heat transfer materialinlet and a particulate heat transfer material outlet and the calcinermay also have a particulate heat transfer material inlet in fluidcommunication with the oxidizer reactor particulate heat transfermaterial outlet, and a particulate heat transfer material outlet influid communication with the oxidizer reactor particulate heat transfermaterial inlet. Hot CaSO₄ discharged by the oxidizer reactor is used inthe endothermic reaction of the calciner and cooled CaSO₄ is dischargedfrom the calciner to the oxidizer reactor.

The shift reactor also includes an H₂ outlet for discharging H₂ from thegasifier. The shift reactor particulate outlet includes a heavies outletdischarging heavy particulates from the shift reactor and a lightsoutlet discharging a mixture of H₂ and light particulates from the shiftreactor. A separator in fluid communications with the shift reactorlights outlet separates the light particulates from the H₂, dischargesthe H₂ from the gasifier, discharges a portion of the light particulatesto the reducer reactor lights inlet and another portion to the calcinerCaCO₃ inlet.

The reducer reactor may also include a char gasifier in fluidcommunication with the shift reactor particulate outlet, a charcombustor in fluid communication with the char gasifier, and a carbonburn-out cell in fluid communication with the char combustor and theoxidizer reactor CaS inlet. The char gasifier includes a heavies inletin fluid communication with the shift reactor heavies outlet, a lightsinlet in fluid communication with the separator, and a hot gas outlet ofthe char gasifier is in fluid communication with a hot gas inlet of theshift reactor. A char outlet and a hot gas inlet of the char gasifierare in fluid communication with a char inlet and a hot gas outlet of thechar combustor. A char outlet and a hot gas inlet of the char combustorare in fluid communication with a char inlet and a hot gas outlet of thecarbon burn-out cell. The carbon burn-out cell includes a CaS outlet influid communication with the oxidizer reactor CaS inlet. Hot CaSO₄ fromthe oxidizer reactor CaSO₄/waste gas outlet is supplied to the carbonburn-out cell and the char combustor and may be supplied to the chargasifier and/or the shift reactor.

The calciner may include a calciner vessel having the CaCO₃ inlet andCaO outlet and a combustor in fluid communication with the calcinervessel, the combustor having an air inlet and a CaS inlet. Air and CaScombusted in the combustor produces hot sorbent particles which aredischarged to the calciner vessel, the heat content of the sorbentparticles calcining the CaCO₃ to produce CaO and CO₂. A settling chamberis disposed intermediate the combustor and the calciner vessel such thathot sorbent particles entrained in flue gas discharged from thecombustor enter the settling chamber, where hot heavy sorbent particlesfall out the flue gas and enter the calciner. The flue gas and entrainedlight sorbent particles are discharged to a first separator, where thefine sorbent particles are separated from the flue gas. The CaO and theCO₂ produced by calcining the CaCO₃ are discharged from the calcinervessel to a second separator. CO₂ produced by calcining the CaCO₃ isalso discharged through a bypass line. A bypass valve controls the CO₂flow distribution between the separator and the bypass line, therebylimiting the exit velocity of the CO₂ to the separator to prevententrainment of heavy sorbent particles in the exiting CO₂. The secondseparator discharges the CaO to the shift reactor.

It is an object of the invention to provide a method which produces amedium Btu syngas without requiring and oxygen plant.

It is also an object of the invention to provide a method which capturescarbon dioxide, generated during production a medium Btu syngas, moreefficiently than conventional methods.

Other objects and advantages of the invention will become apparent fromthe drawings and specification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood and its numerous objectsand advantages will become apparent to those skilled in the art byreference to the accompanying drawings in which:

FIG. 1 is a simplified schematic diagram of a first embodiment of agasifier, having CO₂ removal and hydrogen production, in accordance withan embodiment of the invention;

FIG. 2 is a simplified schematic diagram of the calciner of FIG. 1;

FIG. 3 is a simplified schematic diagram of a second embodiment of agasifier, having CO₂ removal and hydrogen production, in accordance withan embodiment of the invention;

FIG. 4 is a schematic diagram of the fuel flow path of FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to the drawings wherein like numerals represent likeparts throughout the several figures, a gasifier in accordance with thepresent invention is generally designated by the numeral 10. Thegasifier 10 includes chemical process loops, where calcium basedcompounds are “looped” to extract oxygen from air and where CO₂ isextracted from reformed synthetic gas (“syngas”) to produce hydrogen(H₂), and thermal process loops, where solid particulates transfer heatfrom exothermic oxidation reactions to endothermic reduction reactions.

As shown in FIG. 1, the first chemical process loop is a calciumsulfide/calcium sulfate (CaS/CaSO₄) loop 12. The process equipment inthe CaS/CaSO₄ loop 12 includes an exothermic oxidizer reactor 14, anendothermic reducer reactor 16, and a heat exchanger 18. Conventionalpiping, ductwork, and material transport apparatus interconnect thesemajor components 14, 16, 18 of the CaS/CaSO₄ loop 12 as described ingreater detail below. Calcium sulfide and hot air are fed along paths20, 22 through inlets 24, 26 into the oxidizer reactor 14 where the CaSis oxidized at a temperature of 1600 to 2300° F. to form CaSO₄ which isdischarged at a location 28 from the oxidizer reactor through an outlet30. The CaSO₄ is separated from the waste gas components (principallyN₂) of the air fed along the path 22 into the loop 12 in a separator 31.The CaSO₄, heated by the exothermic reaction in the oxidizer reactor 14,and carbon bearing fuel, preferably in the form of coal, are fed alongpaths 28, 90 into the reducer reactor through inlets 32, 34. In anendothermic reaction occurring at a temperature of 1200 to 2000° F., thecoal strips the oxygen from the calcium sulfate to form calcium sulfide,a syngas rich in carbon monoxide (CO) and H₂. The CaS is dischargedalong a path 36 from the reducer reactor 16 through an outlet 38 whichis connected to a separator 37, where the CaS is separated from thesyngas, the CaS being discharged to the inlet 24 of the oxidizer reactor14, to complete the loop 12. A heat exchange unit 39 may be disposedwithin the reducer reactor 16 to produce steam.

A portion of the calcium carbonate (CaCO₃) added along a path 40 to thecalciner 42 (described in greater detail below) is carried over along apath 44 (as CaO) to the first chemical process loop 12 to capture fuelbound sulfur, forming CaSO₄. CaSO₄ which is excess to the looprequirements is discharged along the path 46 from either the oxidizerreactor 14 or the reducer reactor 16 to maintain the mass balance of thechemical reactions. The continuous requirement to capture fuel-boundsulfur to form CaSO₄ regenerates the calcium compounds used in the firstchemical process loop 12, keeping the chemical reactivity high.Depending on the mass flow rate, the heat content of the CaSO₄ may besufficient to maintain the heat balance between the exothermic oxidizerreactor 14 and the endothermic reducer reactor 16. If the mass flow rateof the CaSO₄ is insufficient to maintain the heat balance, inert bauxite(Al₂O₃) particles may be circulated along paths 28, 36, 20 between theoxidizer reactor 14 and the reducer reactor 16 to increase the totalmass of the heat transfer medium.

The heat exchanger 18 includes a hot end 48 having syngas and waste gasinlets and an air outlet, a cold end 50 having syngas and waste gasoutlets and an air inlet, and heat transfer material disposed betweenthe hot and cold ends defining flow passages between the syngas inletand outlet, the waste gas inlet and outlet, and the air outlet andinlet. The syngas (CO) inlet is connected to the syngas outlet of thereducer reactor 16, the waste gas inlet is connected to the waste gasoutlet of the oxidizer reactor 14, and the air outlet is connected tothe air inlet of the oxidizer reactor 14. The heat content of the syngasand waste gas is transferred to the air delivered to the oxidizerreactor by the heat transfer material of the heat exchanger 18,improving the efficiency of the exothermic reaction in the oxidizerreactor 14.

In the first chemical process loop 12, the amount of oxygen in the airdelivered to the coal is only sufficient for partial oxidation. In thiscase, the end product is a sulfur free syngas rich in carbon monoxide(>300 Btu/ft³) suitable for a gas turbine combined cycle. Alternatively,when the amount of oxygen supplied is sufficient to burn all of thecoal, the loop acts as a combustion system having end products of pureCO₂ and steam.

The second chemical process loop is a lime/calcium carbonate (CaO/CaCO₃)loop 52. The process equipment in the CaO/CaCO₃ loop includes a calciner42 and a water-gas shift reactor 54. Conventional piping, ductwork, andmaterial transport apparatus interconnect these components as describedin greater detail below. Steam, lime (CaO), and the CO rich syngasproduced in the CaS/CaSO₄ loop 12 are fed along paths 56, 58, 60 throughinlets 62, 64, 66 into the shift reactor 54 where, the CO of the syngasreacts with the gaseous H₂O to produce H₂ and CO₂. The lime captures theCO₂, forming CaCO₃ in an exothermic reaction, producing a temperaturelevel of 1200-1700° F. This heat can drive a gasification reaction ofthe entering fuel and gas and may generate, as schematically shown atlocation 68, high temperature steam for a steam turbine.

The CaCO₃ and H₂ are each discharged along paths 70, 72 from the shiftreactor 54 through an outlet 74, 76. The H₂ is received in a separator77, where any fines entrained in the flow of H₂ are removed anddischarged along a path 79 to the shift reactor 54. A compressor 78 inthe syngas discharge line 80 pressurizes the H₂ to a sufficient level toinject the H₂ into a gas turbine, fuel cell or other hydrogen usingprocess. The CaCO₃ is transported to the calciner 42 to drive off CO₂gas and to regenerate CaO which is then returned along a path 58 to theshift reactor 54 to capture more CO₂, completing the loop 52. Capture ofthe CO₂ by the production of CaCO₃ drives the endothermic gasificationreaction between the carbon dioxide, water and fuel to produce a greaterquantity of carbon monoxide and hydrogen and to limit the amount of heatwhich must be removed (by producing steam 68). The hydrogen is producedby the water gas shift reactionCO+H₂O⇄CO₂+H₂and the carbon dioxide is captured by the reactionCaO+CO₂→CaCO₃

When the two chemical process loops 12, 52 and thermal process loops 82,83; 84, 85 are combined, a coal to hydrogen chemical process 88 isformed where the CaO required by the reducer reactor 16 is produced bythe calciner 42, the CO rich syngas required by the shift reactor 54 isproduced by the reducer reactor 16, and the heat required by thecalciner 42 is produced by the oxidizer reactor 14 (described in greaterdetail below). The gasifier 10 and process for producing hydrogen 88disclosed herein is more efficient than the oxygen blown IGCC process,the parasitic power loss of the oxygen plant, the heat losses associatedwith water-gas shift cooling, and the low temperature sulfur recoveryassociated with the IGCC process outweighing the need for a syngascompressor 78 in the subject gasifier 10.

The calciner 42 in the CaO/CaCO₃ loop 52 is a high temperatureendothermic reactor that receives its heat from the oxidizer reactor 14in the CaS/CaSO₄ loop 12. In a first embodiment of a thermal processloop 82, 83 transferring heat from the oxidizer reactor 14 to thecalciner 42 (FIG. 1), a heat exchange mass in the form of inertparticles, such as bauxite (Al₂O₃) particles or sorbent (CaO, CaCO₃,CaS, CaSO₄) particles is circulated 82, 83 between the oxidizer reactor14 and the calciner 42 via interconnecting piping. The bauxite, CaO,CaS, and CaSO₄ is chemically inert in the calciner and can be separatedfrom the reactants of either chemical process loop 12, 52 allowing theheat to be balanced independent of the mass balance of the chemicallyactive material. Any bauxite which is lost during the operating cycle ofthe gasifier 10 may be made-up by adding, along the path 90, new bauxiteparticles through an inlet 34 to the reducer reactor 16.

With reference to FIGS. 3 and 4, sorbent (CaO, CaCO₃, CaS, CaSO₄)particles and coal (carbon) particles are the primary heat transfer massin a second embodiment of the gasifier 10′. Bauxite particles may beutilized to provide for any heat transfer mass that is required foroperation but which is not provided by the sorbent and coal particles.The raw coal utilized by the gasifier 10′ is fed along a path 92 intothe shift reactor 54 through an inlet (along with the lime and steam 94,96). The high temperature generated by the exothermic reaction producingthe CaCO₃ devolatize and partially decarbonate the coal, with theresulting char, in the form of “heavies” and “lights”, being dischargedalong paths 98, 100 from the shift reactor 54 through a pair of outlets102, 104 which are connected to a pair of inlets 106, 108 on the reducerreactor 16. CaCO₃ particles, in the form of lights, are also discharged100 from the shift reactor 54. The flow of lights is received in aseparator 110, where the small particles of char and calcium carbonateare separated from the hydrogen in which they are entrained. The lightsand the hydrogen are discharged along paths 112, 114 from the separator110, with the hydrogen being piped to the hydrogen discharge 72 of theshift reactor 54 and the lights joining the large char particles (theheavies) in the reducer reactor 16. A portion of the small charparticles and CaCO₃ may be fed along a path 113 to the calciner 42 toregenerate CaO and separate CO₂. A heat exchange unit 115 may bedisposed between the shift reactor 54 and the compressor 78 to producesteam.

In the thermal process loop 84, 85 of this embodiment 10′, the reducerreactor 16 comprises three sections, a char gasifier 116, a charcombustor 118 and a carbon burn-out cell 120. As shown in FIG. 4, thechar gasifier heavies and lights inlets 106, 108 are connected to theshift reactor heavies outlet 102 and the separator lights outlet 122 asdescribed above. In addition, a gas outlet 124 of the char gasifier 116is connected to a gas inlet 126 of the shift reactor 54 and a gas inlet128 and a char outlet 130 of the char gasifier 116 are connected to agas outlet 132 and a char inlet 134 of the char combustor 118. The charcombustor 118 also has a char outlet 136 connected to a char inlet 138of the carbon burn-out cell 120, a gas inlet 139 connected to a gasoutlet 141 of the carbon burn-out cell 120, and a CaSO₄ inlet 140connected to an outlet of the oxidizer reactor 14. The carbon burn-outcell 120 also has a CaS/fuel outlet 142 connected to an inlet of theoxidizer reactor 14, preferably has a CaSO₄ inlet 144 connected to anoutlet of the oxidizer reactor 14, and may have an air inlet 146.

As described above, the oxidizer reactor 14 produces CaSO₄ in anexothermic reaction. The heat produced in this reaction is absorbed bythe CaSO₄ and is transported 28 with the CaSO₄ to the reducer reactor16. A portion of the flow of hot CaSO₄ is preferably split into threestreams, with a small portion of the hot CaSO₄ being fed along a path148 to the carbon burn-out cell 120 and larger portions of the hot CaSO₄being fed along paths 150, 153 to the char combustor 118 and, whennecessary, to the char gasifier 116. The heat and oxygen content of thehot CaSO₄ decarbonizes the char received in the carbon burn-out cell120, completing the decarbonization of the coal and producing a CO₂ richgas which is discharged along a path 151 to the char combustor and coolCaS which is discharged along a path 152 to the oxidizer reactor 14. Theheat and oxygen content of the hot CaSO₄ partially decarbonizes the charreceived in the char combustor 118, producing hot CO₂, CO and H₂O. Theremaining char is discharged along a path 154 to the carbon burn-outcell 120 and the hot gases are discharged along a path 156 to the chargasifier 116. The heat and oxygen content of the hot gases (and CaSO₄when fed along a path 153 to the char gasifier 116) partiallydecarbonizes the char received in the char gasifier 116, producing hotH₂ and hot CO rich syngas. The remaining char is discharged along a path158 to the char combustor 118 and the hot gases (including any remaininghot CO₂ and hot H₂O) are discharged along a path 160 to the shiftreactor 54.

It should be appreciated that staged gasification of the coal with thecoal solids and coal gases moving in counterflow provides an efficientmeans to maximize carbon conversion/minimize unburned carbon andmaximize the production of H₂ and CO gas while also providing anefficient means for transferring the heat energy produced by theoxidizer reactor to both the reducer reactor 16 and the shift reactor54. It should be further appreciated that the hot gases fed along a path160 from the char gasifier 116 to the shift reactor 54 will further heatthe CaCO₃ which is fed along a path 70 from the shift reactor 54 to thecalciner 42, thereby reducing the heat energy required to perform thecalcination process. If additional heat input is required for thecalciner 42, hot CaSO₄ may be fed along a path 162 from the oxidizerreactor 14 to the shift reactor 54. Alternatively, bauxite or otherinert particles may be circulated between the oxidizer reactor 14 andthe calciner 42 via the shift reactor 54.

In an alternative embodiment, the calciner 42′ may include a combustor166 in which air and CaS are combusted to produce additional heat forthe calciner 42′ (FIG. 2). Particles of hot sorbent entrained in theflue gas are discharged along a path 168 from the combustor 166 andenter a settling chamber 170, where the heavy hot solids fall out alonga path 172 of the flue gas and exit the settling chamber via a slopedduct 174. The flue gas and entrained lights are discharged along a path176 to a separator 178, where the fines are separated from the flue gas.The hot heavy solids are fed by the duct 174 into the calciner vessel180, along with the cool CaCO₃ and hot bauxite particles (if beingused). The heat from the heavy solids and bauxite particles calcines theCaCO₃, producing CaO and CO₂ (for subsequent use or sequestration).

The hot heavy solids, CaCO₃ and hot bauxite particles are introducednear the bottom of the calciner vessel 180, CO₂ is released therebyforcing the cooling heavy solids, cooling bauxite and the CaCO₃/CaOupwards along a path 182. The cold heavy solids and cold bauxite spillover a location 184 the side of the calciner vessel 180 and are fedalong a path 186 to the combustor 166 by a spillway 188. The coldbauxite is returned along a path 190 to the oxidizer reactor 14 forheating and the heavy solids are further combusted in the combustor 166.The relatively light CaO is entrained in the CO₂, the combined CaO andCO₂ being discharged along a path 192 from the calciner vessel 180 to aseparator 194 which removes the CaO from the CO₂. A portion of the CO₂is removed along a path 196 from the calciner vessel 180 by a filter 198which prevents the CaO entrained therein from also being removed. Avalve 200 in the bypass line 202 controls the volumetric flow of CO₂through the bypass line 202, thereby controlling the CO₂ flowdistribution between the separator 194 and the bypass line 202 andcontrolling the exit velocity of the CO₂ to the separator 194 to prevententrainment of heavy solids in the exiting CO₂.

To maintain the efficiency of the chemical process loops describedabove, it is important to maintain the sorbent activity of the chemicalsutilized in the chemical process loops 12, 52. As discussed above, fuelbound sulfur is continuously captured in the CaS/CaSO₄ loop 12,requiring continuous removal at a location 46 of CaSO₄ and continuousaddition at a location 40 of CaCO₃. The CaCO₃ is removed from theCaO/CaCO₃ loop 52, requiring the continuous addition at a location 94 ofCaO. The continuous replenishment at the location 94 of CaOsubstantially regenerates the calcium compounds used in the gasifier 10,keeping the chemical reactivity high. In addition, the sorbent activityof the chemicals is enhanced by the reduction reactions and hydrationreactions employed in the chemical process loops 12, 52, which weakenthe CaSO₄ and CaCO₃ shells. The CaO produced by the calciner 42 passesthrough an activator 204 which mechanically breaks the particle,exposing additional surface. The activator 204 includes an eductor wherea portion of the flow of CaO is entrained in a flow of gas andaccelerated thereby. The entrained CaO is impacted against a surface ofthe activator 204, the impact mechanically fracturing the particles,assisted as necessary by steam or water hydration 206.

While preferred embodiments have been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustration and not limitation.

The invention claimed is:
 1. A system for producing a gas product from acarbonaceous fuel in a gasifier, the system comprising: an oxidizerreactor that oxidizes CaS in air therein to form hot CaSO₄; a reducerreactor that receives the hot CaSO₄ and a carbonaceous fuel wherein thehot CaSO₄ and the carbonaceous fuel undergo an endothermic reactiontherein and utilizing heat content of the hot CaSO₄ to form CaS and agas product; an inlet to supply oxygen to the reducer reactor in asufficient amount for substantially complete combustion of thecarbonaceous fuel such that the gas product is substantially all CO₂ andsteam; and a first separator that receives a gas flow from the reducerreactor, wherein the gas flow includes the gas product and entrainedCaS, and separates the gas product and entrained CaS of the gas flow,wherein the separated CaS is provided to the oxidizer reactor for use inthe oxidizing.
 2. The system of claim 1, wherein the reducer reactorreceives a calcium oxide bearing compound.
 3. The system of claim 2,wherein the calcium oxide bearing compound includes CaCO₃.
 4. The systemof claim 2, wherein the calcium oxide bearing compound includes CaO. 5.The system of claim 1, wherein the oxidizer reactor oxidizes CaS in airtherein to further form a waste gas; and further comprising: a secondseparator that separates the hot CaSO₄ and the waste gas, wherein theseparated CaSO₄ is provided to the reducer reactor.
 6. The system ofclaim 5, wherein the waste gas includes principally nitrogen.
 7. Thesystem of claim 5, further comprising: a heat exchanger using heatcontent of the waste gas to heat the air provided to the oxidizerreactor.
 8. The system of claim 5, wherein a portion of the hot CaSO₄ isdischarged after separating the hot CaSO₄ and the waste gas.
 9. Thesystem of claim 1, further comprising a heat exchanger to use the heatcontent of a waste gas to heat the air.
 10. The system of claim 1,wherein the reducer reactor includes an exit at an upper portion of thereducer reactor from which the gas flow exits to the first separator.11. The system of claim 1, further comprising: a heat exchanger thatuses the heat content of the gas product to heat the air, wherein theheated air is provided to the oxidizer reactor.
 12. The system of claim1, further comprising a regenerative heat exchanger to heat the air fromusing the heat content of the gas product to produce heated air.
 13. Thesystem of claim 1, further comprising a heat exchange unit to heat thewater using the heat content of the hot CaSO₄ to produce a flow ofsteam.
 14. The system of claim 1, wherein the carbonaceous fuel includessulfur.
 15. The system of claim 1, wherein the oxidizer reactor includesCaO that captures sulfur to form CaSO₄.
 16. The system of claim 1,wherein the reducer reactor is formed of a single chamber.
 17. Thesystem of claim 1, wherein the oxygen is provided by an air stream. 18.The system of claim 1, wherein the oxygen is provided by a calcium oxidebearing compound.
 19. A system for producing a gas product from acarbonaceous fuel in a gasifier, the system comprising: an oxidizerreactor oxidizing CaS in air therein to form hot CaSO₄; a reducerreactor that receives the hot CaSO₄ and carbonaceous fuel wherein thehot CaSO₄ and the carbonaceous fuel undergo an endothermic reactiontherein utilizing heat content of the hot CaSO₄ to form CaS and a gasproduct; an inlet to supply oxygen to the reducer reactor in an amountof oxygen for partial oxidation of the carbonaceous fuel such that thegas product is syngas; and a first separator that receives a gas flowfrom the reducer reactor, wherein the gas flow includes the gas productand entrained CaS, and separates the gas product and entrained CaS ofthe gas flow, wherein the separated CaS is provided to the oxidizerreactor for use in the oxidizing.
 20. The system of claim 19, whereinthe syngas is rich in carbon monoxide.
 21. The system of claim 19,wherein the reducer reactor further receives a calcium oxide bearingcompound.
 22. The system of claim 19, wherein the oxidizer reactoroxidizes CaS in air therein to further form a waste gas; and furthercomprising: a second separator that separates the hot CaSO₄ and thewaste gas, wherein the separated CaSO₄ is provided to the reducerreactor.
 23. The system of claim 19, wherein the reducer reactorincludes an exit at an upper portion of the reducer reactor from whichthe gas flow exits to the first separator.
 24. The system of claim 19,wherein the reducer reactor is formed of a single chamber.
 25. Thesystem of claim 19, wherein the oxygen is provided by an air stream. 26.The system of claim 19, wherein the oxygen is provided by a calciumoxide bearing compound.
 27. A system for producing a gas product from acarbonaceous fuel in a gasifier, the system comprising: an oxidizerreactor oxidizing CaS in air therein to form hot CaSO₄; a reducerreactor that receives the hot CaSO₄ and a carbonaceous fuel wherein thehot CaSO₄ and the carbonaceous fuel undergo an endothermic reactiontherein utilizing heat content of the hot CaSO₄ to form CaS and a gasproduct; and a first separator that receives a gas flow from the reducerreactor, wherein the gas flow includes the gas product and entrainedCaS, and separates the gas product and entrained CaS of the gas flow,wherein the separated CaS is provided to the oxidizer reactor for use inthe oxidizing.
 28. The system of claim 27, wherein the oxidizer reactoroxidizes CaS in air therein to further form a waste gas; and furthercomprising: a second separator that separates the hot CaSO₄ and thewaste gas, wherein the separated CaSO₄ is provided to the reducerreactor.
 29. The system of claim 27, wherein the reducer reactorincludes an exit at an upper portion of the reducer reactor from whichthe gas flow exits to the first separator.